Angiogenesis plays a crucial role in numerous physiological processes and in a wide variety of pathological conditions of human diseases, including ischemic vascular diseases, atherosclerosis, tumor growth and metastasis, diabetic retinopathy, age-related macular degeneration, and rheumatoid arthritis. Hence identification of key angiogenesis regulators may lead to develop more specific and efficacious new therapies for treating angiogenesis-associated human diseases. We have recently reported that the serine/threonine protein kinase D2 (PKD2) plays a pivotal role in endothelial cell (EC) proliferation, migration, and in vitro angiogenesis in part through modulation of the expression of vascular endothelial growth factor (VEGF) receptor-2 and fibroblast growth factor receptor-1 and the production of proangiogenic cytokines. We have also accumulated substantial new evidence indicating that PKD2 is essential for the expression of numerous other important proangiogenic growth factor receptors, receptor ligands, and plasma membrane enzymes in ECs. Our novel findings are cited and strongly supported by a recent publication from other group showing that PKD2 is a crucial regulator of tumor-induced angiogenesis in vivo. However, it is not known whether PKD2 plays a major role in angiogenesis in vivo under other pathological or physiological conditions, and the molecular basis of PKD2-mediated angiogenesis in vivo is still not clear. Especially, whether PKD2 regulates the proangiogenic functions of macrophages has not been explored. This resubmission R21 proposal is designed to answer these important questions with the following two Specific Aims: Aim 1) To determine PKD2 function and signaling in angiogenesis induced by VEGF-A or multiple proangiogenic growth factors using in vivo Matrigel angiogenesis assay; Aim 2) To determine the role and molecular basis of PKD2 in angiogenesis using a mouse model of hind-limb ischemia. This resubmission R21 proposal will identify PKD2 as a novel and key regulator of angiogenesis in vivo and will provide new insights into the PKD2-mediated angiogenesis. In addition to its role in ECs, this proposal will identify a novel function of PKD2 in macrophage proangiogenic responses by hypoxia and proangiogenic growth factors. We anticipate that these studies will provide a strong rationale for PKD2 as a novel drugable target for therapeutic intervention in angiogenesis- related human diseases.